Recently, the consequences of a step in a fluid of strongly interacting radiation (SIDR) was investigated in the context of the \(H_0\)  tension [1]}. The \(H_0\)  tension is the \(4.8\sigma \)  disagreement between the measurement of the local expansion rate based on late-universe observables, in particular Cepheid-calibrated Type IA supernovae from SH0ES [2]} \(H_0=73.04\pm 1.04\,\) km/s/Mpc when compared against inferences based early universe physics, such as from the CMB alone or in combination with BAO \(H_0=67.27\pm 0.60\,\) km/s/Mpc [3]}. A broad variety of proposals have been presented in attempts to reconcile this, see., e.g., [4]}, [5]}, [6]}, [7]}, [8]}, [9]}, [10]}, [11]}, [12]}, [13]} and additional models summarized in [14]}. One common group of models include additional radiation [15]}, [16]}, [17]}, [18]}, [19]}, [20]}, [21]}, [22]}, [23]}, [24]}, [25]}, which may be strongly interacting. In [1]}, it was shown that the presence of a mass threshold in a fluid of SIDR allowed for a higher value of \(H_0\)  and a better overall fit to a broad set of data. In particular, the data preferred a mass threshold occurring near \(z_t \sim 20\,000\) .
